This invention relates to an apparatus for recoiling metal strips which are produced when a coil of sheet metal is slit parallel to its longitudinal axis. Particularly when slitting large coils of thin sheet, metal uneven thickness over the width of the sheet will often result in the slit strips differing in length. It is usual when rolling metal sheet and metal foil that the thickness of the product varies across its width, and the result of this is that the metal strips which are cut along the length of the sheet are longer where the sheet is thin than where it is thicker. As a result, when several strips are recoiled into a common mandrel with the same rotational speed along its entire length, the coils containing the longest strips will be loosely wound.
German Auslegeschrift No. 2,933,775 attempts to solve this problem by dividing the recoiler mandrel into sections, so that it consists of a number of cylinders, or drums, suspended on a common shaft, friction blocks being placed inside the sections, so arranged that the friction can be varied by varying pneumatic or hydraulic pressure, enabling the sections, to a certain extent, to rotate at different speeds. This system requires a very exacting control of the pressure as the coils of strip build up. To avoid uneven strip tension, the operator will ensure that the friction surfaces for all the sections are continuously sliding against one another. This is difficult to achieve, and can result in surface scratches and uneven coiling.
A corresponding solution to the problem is that the friction elements consist of friction discs placed between the sections, the friction force being varied by pressing the sections together by axial hydraulic or pneumatic pressure. This solution also gives, in principle, different coiling tensions, and has the same disadvantages.
A third solution is discussed by N. P. Rutledge, "Iron and Steel Engineer", February 1971 pages 70-71. Here, constant coiling tension is achieved by means of magnetic braking of the coils, but to take care of the differences in length, an accommodating unit is required, and this is in the form of a deep pit in which the strip hangs in a loop. If the strips are long, the loop may hang several meters down into the pit. Furthermore, the friction element here can also result in surface damage.